The v-mht forms, with the Deltagag sequences of MH2, a fused gene which is in all likelihood a transforming gene. Sequences related to the v-mht oncogene are present in the genomes of normal chicken and of many mammalian species (including man). This oncogene is expressed as a unique RNA species of approximately 4 kb. Studies of the chicken mht have been initiated to determine its real transcriptional and translational boundaries.